1. Technical Field
The present invention relates to a fuel cell system for generating electric power through a reaction of fuel and oxidation gas (hereinafter, referred to as “electric power generation reaction”).
2. Description of the Related Art
Recently, it has been promoted to use a fuel cell as an electric power generation part of a fuel cell distributed electric power generation system, since even a small fuel cell has high electric power generation efficiency. In order to allow the fuel cell to function as an electric power generation part of the distributed electric power generation system, fuel is required to be supplied stably. In a general fuel cell, fuel such as natural gas, city gas, liquefied petroleum gas, gasoline, or kerosene is supplied to generate a reformed gas containing hydrogen through a reforming reaction of water vapor and the fuel with a Ru catalyst or a Ni catalyst under a temperature of 600 degrees Celsius-700 degrees Celsius. The reformed gas is used as fuel of the fuel cell. The reaction heat necessary for the reforming reaction can be obtained, for example, by combusting an anode off-gas which has not been used in the anode of the fuel cell.
In order to improve electric power generation efficiency of a fuel cell system, it is required to improve the usage efficiency of the fuel and to use exhaust heat exhausted in the operation of the fuel cell with economy. A solid oxide fuel cell comprises stacks each of which is operated under a high temperature of 650 degrees Celsius-900 degrees Celsius. In order to improve the electric power generation efficiency of the solid oxide fuel cell, it is important to effectively use the exhaust heat generated in the operation of the fuel cell. As shown in FIG. 8, Japanese Patent Application Laid-open Publication No. 2011-216308A discloses a solid oxide fuel cell system comprising an evaporator 903, a desulfurizer 902, a reformer 904, a fuel cell part 906, and a combustor 907 in a heat-insulative housing 901. An inner housing 916 contained in the heat-insulative housing 901 contains the evaporator 903, the reformer 904, the fuel cell part 906, and the combustor 907. In the solid oxide fuel cell system disclosed in Japanese Patent Application Laid-open Publication No. 2011-216308A, an anode off-gas is combusted at the combustor 907 to heat the evaporator 903 and the reformer 904 using the combustion heat thus obtained. The combustion heat transfers to the desulfurizer 902 provided outside of the inner housing 916, and the desulfurizer 902 is heated by the combustion heat thus transferred.